The present invention relates generally to inductors, and, more specifically, to a high performance inductor incorporating carbon nanotubes in its construction.
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but process about it, in random order, at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, MZ, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
MR receiver coils receive the emitted signals and use the acquired signals for image reconstruction. The MR receiver coils typically use individual passive elements such as inductors in their RF circuitry. However, existing inductor constructions are often too large, in area and volume, to incorporate into high channel count of small designs where miniaturization is desired.
Carbon nanotubes have been developed in recent years and show promise for a multitude of products because of their unique properties. Among the properties is a high electrical conductivity thereby enabling the carbon nanotube to carry a very high electrical current density. Current carrying capabilities of bulk carbon nanotubes typically exceeds that of copper by 2.5 to 6 times. Additionally, carbon nanotubes exhibit high thermal conductivity, up to for instance 4000-6000 W/m-K.
Inductors are typically constructed with an electrically conducting material, such as copper, formed in a magnetic flux-concentrating pattern such as a coil. Typically, the electrically conducting material is wrapped about a core such as air or a ferromagnetic material. When electrical current is passed through the conductor, a magnetic field is induced about the conductor and core. The coil arrangement concentrates the induced magnetic field, thereby creating an inductance, L. A time-varying current,
            ⅆ              i        ⁡                  (          t          )                            ⅆ      t        ,passing through the conductor will cause a time-varying voltage, v(t), across the inductor, as described by the following differential equation:
                              v          ⁡                      (            t            )                          =                  L          ⁢                                                    ⅆ                                  i                  ⁡                                      (                    t                    )                                                                              ⅆ                t                                      .                                              (                  Eqn          .                                          ⁢          1                )            The Q factor quantifies the performance of an inductor in an electrical circuit:
                    Q        =                              wL            R                    .                                    (                  Eqn          .                                          ⁢          2                )            As such, loss of inductive quality occurs when resistance of the electrical conductor is increased or when inductance, L, is decreased. Reduced Q factor thereby causes reduced performance of an electrical circuit, and in particular, an electrical circuit in a RF receiver coil of a MR system. Additionally, use of a ferromagnetic core material in an inductor is not compatible with use in an MR system. Increasingly, there is a demand for inductors in RF circuits with both improved Q factor and reduced area and volume.
It would therefore be desirable to have an inductor with increased Q factor, while also obtaining such performance improvement with reduced area and volume.